This invention relates to a wall anchor and particularly to a wall anchor comprising a socket having a body portion with fingers integrally hinged thereto and also comprising a drive pin that can be driven into the socket to spread the fingers by a camming action. The invention further relates to a wall anchor that can attach a part to a wall and that incorporates means to retain the wall anchor on the part prior to attachment to the wall.
Various wall anchors, including those with laterally expandable fingers, have been devised. These earlier wall anchors have been made of various materials, including plastic. However, there are unique features of this invention, which include a socket that is a unitary molded plastic member having a head on one end, a body section in the center, and fingers hinged at the other end, outwardly projecting barbs spaced from the head, with a passage through the head and body communicating with the fingers, wherein the fingers have transverse walls in the path of the passage, combined with a pin that can be driven by a hammer through the passage into contact with the transverse walls to act as a cam and pivot the fingers laterally outwardly.
The transverse walls are preferably inclined inwardly and toward the head of the socket so that the pin will pivot the fingers as far outwardly as possible toward ninety degree projections relative to the axis of the passage.
A special feature of this invention is the provision of a web slightly spaced from the transverse walls. There is a small opening through the web, such as a slit. Without the web, a stress line would be formed during molding, the end of the core forming the passage where that core intersects the transverse walls. By providing the web, the location of the stress line is moved to the intersection of the core and the web, and the walls joining the web and the transverse walls can be formed rounded with no stress lines. This avoids failure at the pivot lines of the fingers that might result from stress lines.
The web performs another function. As the drive pin is driven through the passage, it first contacts the web and, because the slit is parallel to the pivot lines of the fingers, the pin will split the web and pivot its halves toward the fingers. Thereafter, when the pin cams the fingers outwardly, the web halves lie against the pin and present edges opposing a tendency of the transverse walls to slide back along the pin. A particular advantage in the present wall anchor is that it is molded with the fingers positioned together. Therefore, it is not necessary to squeeze the fingers together to insert the socket into a pre-drilled hole in a wall.
Additional features of this wall anchor which are distinctive include longitudinal ribs on the inner wall of the passage to grip the shank of the drive pin, barbs on the outer wall of the shank, adjacent the head thereof, to snap the socket within a hole provided in another part that is to be secured to a wall surface, a head on the socket that acts as a positive stop against the wall surface or against the part, sawtooth rings on the outer body surface of the socket to frictionally engage a hole in a wall, and ridges on the outer surfaces of the fingers that frictionally engage the wall when the fingers are laterally extended. These ridges are on generally flat outer faces of the fingers which therefore maintain maximum contact area with the wall surface when the fingers are spread and laterally extended. However, the outer longitudinal corners of the fingers are chamfered to keep the fingers within the general overall diameter of the socket, and within the overall diameter of a hole in the wall into which the socket is to be mounted. The leading end of each finger is tapered to facilitate introduction of the socket into the hole in the wall.
In addition to these important features of the socket, the pin is also distinct in that it comprises a lead section that is generally like a nail. This lead section is normally held within the ribbed portion of the passage in the socket in a ready position. The trailing end of the drive pin has a head on it with a kerf in it that is sized to receive a screwdriver, or a phillips head slot, and adjacent the head, the drive pin preferably has threads that are typically in a double helix. The threads have a sawtooth contour so that the drive pin can be driven in the direction of its lead end but will respond to a screwdriver when rotated in a counter clockwise direction to withdraw the pin from the socket.
The drive pin may have a sharp point on its lead end, as a nail point, or it may be rather blunt, or semi-spherical. The semi-spherical point functions well to avoid the aforesaid wedging between the fingers, cooperating with the inclined transverse walls to produce the desired camming action. If a point is used, is should be driveable into a wood stud, but not too sharp to jam between the fingers and avoid the camming action.
On the other hand, an advantage of the pointed drive pin is that, if the anchor is placed in a predrilled hole in a stud that restrains the fingers from pivoting laterally, the sharp point will lead the pin into a wedging position between the fingers and wedge them tightly against the side walls of such a hole. In such a use, the edges of the outer surfaces of the fingers are particularly effective in holding the anchor in place, and the sawtooth configuration of these ridges is an additional aid in the effectiveness of the grip.
The invention provides an inexpensive wall anchor in that the socket is a single piece and can be readily produced by molding plastic. The camming action between the drive pin and the transverse walls on the fingers produces maximum spread of the fingers and results in a stronger installation on the wall. The barbs spaced from the head allow the socket to be snapped in place and held in the hole of a part that is to be mounted on the wall. The longitudinal ribs hold the drive pin in the socket but withdrawn from the fingers so the socket can be pushed into a hole in the wall.